Engraver&#39;s gum



Sept, 12, 1944. E. A. sPRlGG rs1-AL ENGRAVERS GUM Filed Aug. 1,l 1940 FJ?? Ea 5.1? @Wag-g5 E Patented Sept. 12, 1944 ENGRAVERS GUlVI Edward A. Sprigg, Wadsworth, and Edgar O. Macy, Cuyahoga Falls, Ohio, assgnors to The B. F. Goodrich Company, New York, N. Y., a corporation of New York Application August 1, 1940', Serial No. 349,356

4 Claims.

This invention relates to engravers gum and is especially useful in the art of printing.

In the printing of many materials such as fabrics, rough surfaced papers, straw board containers, wood, and sheet metal surfaces, it is desirable to provide printing plates of resilient material which will conform to the surface to be printed. For speed and convenience in printing it is desirable to provide flat plates which may be bent and secured to a cylinder of the printing press. Sheet material for this purpose having a printing surface of resilient rubber composition and a backing of textile material has been used for the purpose. The printing face has usually been of rubber material which may be cut away easily or engraved, and its adhesion to the backing has preferably been such that the areas cut from the facing may be peeled clean from the fabric backing. In some cases where the spaces between printing areas are great, more than one removable layer has been provided so that the material may be removed or stripped in steps where desired.

The removal of one or more layers of rubber material over areas of the sheet naturally weakens the sheet and increases its stretchability. It has been proposed to provide the sheet with backing layers of metal to prevent stretching of the sheet but such a construction has not been satisfactory clue to the difficulty of uniformly forming the engraved sheet to cylindrical form, the metal tending to bend more easily at one place than at another, and the fact that the metal is permanently extensible and not, elastic.

It has also been proposed to'use a reinforcel ment of perforated metal with the result that the metal has had the objection of being bent more easily along rows of perforations than at other places and has made the provision of a true cylindrical printing face impossible.

It has also been proposed to use a reinforcement of screen wire or woven wire netting but due to the crimp of the wires the material has been too stretchable and the same difliculties have been encountered as with other metal reinforcements.

While woven fabric has been used as a reinforcing material, the crimp of the threads in the fabric has caused such stretch of the sheet as to permit satisfactory use of such engravers gum only for one color work or in colors when register of diiTerent impressions was not necessary.

The present invention aims to overcome the faults of engravers gum of prior constructions.

The principal objects of the invention are to f 'l provide an improved engravers gum, to provide an engravers gum which may be used effectively for color register printing, to provide increased resistance to stretch, to provide uniform flexibility, and to prevent migration of vulcanizing ingredients from the reinforcing layer to the face material of the sheet.

These and other objects will appear from the following description and the accompanying drawing.

Of the drawing: Y

Figfl is a perspective view of a sheet of engravers gum embodying the invention prepared for printing, the drawing showing the material to a greatly magnified scale for clarity of illustration.

Fig. 2 is a similar view showing another sheet of different construction also embodying the invention.

' In accordance with the invention a stretchresisting backing is provided comprising rubber material prepared to give this characteristic with flexibility. I c

Good results have been obtained by semi-hard rubber composition containing fibrous material i for resisting stretch of the sheet. The invention also contemplates the use of a barrier layer of soft rubber composition to prevent migration of vulcanizing ingredients from the semi-hard rubber composition to the printing and cushioning layers. Y v

Referring to the drawing which illustrates two examples of constructions embodying the invention which may be embodied in many different constructions and is not limited to the embodiment shown, and first with reference to Fig. 1, thev numeral I0 designates the printing face, and theA numeral II the supporting face, of a sheet of engravers gum embodying the invention. At the printing face is an impression layer I2 of resilient close grained material of rubber-like composition. While soft vulcanized rubber compositions maybe employed for this layer which must have the properties of resilience, attraction for the ink employed, resistance to swelling, ease of engravability, and resistance to Wear, where oily or greasy inks are employed it is desirable to employ a synthetic rubber material such as a copolymer of butadiene and acrylonitrile as a base fork compounding this layer as such material has greater resistance to swelling 'and loss of strength when in contact with printers inks.

The lower face of the impression layer I2 is supported by a reinforcing layer I3 of rubberized fabric, and these layers are separable at their interface I4 by a force varying between 4 and 10 pounds per linear inch to permit stripping awayl the areas not desired for printing as indicated at I5. The interface I4 is known as the first stripping level.

When there is great spacing between printingl I1. The layer I6 is known as a cushion layer and may be of the same material as the impression layer I2 or of ordinary soft vulcanized rubber composition having the desired 'cushioning properties and readily capable of being peeled at the second stripping level.

A reinforcing -layer of rubberized fabric I8 is which they are woven provides undesirable.

stretchability of the sheet. To provide-resistance to stretchability, a layer 2Q of relatively nonstretchable rubber compositionis provided between the layers I8 and I9. This layer is formed of a semi-hard rubber composition having a high percentage of straight unwoven bers 2i extending in the plane ofthe sheet and preferably having considerable overlap of the fibers. A suitable composition may be prepared vby grinding and milling unvulcanized trimmings of rubberized cord or fabric removed from tires and other rubber and fabric articles and adding suitable vulcanizing ingredients such as sulfur to increase the hardness of the resulting composition. The milling and sheeting of the material in a thin layer of about .030 inch thickness lays the Vbers in the direction of the sheet and in overlapping relation While the semi-hard rubber provides additional resistance to stretch and binds the fibers together to provide a substantially non-stretchable layer while, at the same time, the fibers reduce shrinkage of the semihard rubber composition.

To provide against migration of the sulfur and other vulcanizing ingredients from the layers 20 to the cushion layer I6, which migration might cause hardening of such cushion layer and increase resistance to strippirg it from the fabric layer I8, a thin layer 22 of soft rubber composition low in sulfur content is employed as a barrier layer on the under side of the fabric layer I8 to Whichit may be applied by calendering, whereby the barrier layer through its ability to absorb vulcanizing ingredients retards migrationV of the latter to the printing and cushioning layers.

As it is necessary to hold the thickness of the material within close limits, a surfacing layer 23 of rubber composition is provided at the supporting face. This layer is of material which may be ground away to provide the desired thickness without wooling up. A rubber composition similar to the material of wringer: rolls is suitable for this purpose as it may be ground away leaving a smooth level surface. Preferably this layer contains a high percentage of materials such as factice and Whiting which facilitate grinding thereof.

VIn the embodiment of the invention illustrated in Fig. 2, the cushion and second stripping level are omitted. The impression layer 3|! is of the same composition as the layer I2 of Fig. 1 and is mounted on a layer 3| of fabric providing a stripping level 32 at the interface. The layer 33 is of the same brous semi-hard rubber composition as the layer 20 of Fig. 1 and the barrier layer 34, fabric layer 35, and surfacing layer 36 correspond to the layers 22, I9, and 23 respectively of Fig. 1.

In either of the embodiments shown the fibrous thick the barrier layer 22 or 34 may be omitted.

Variations may be made without departing from thescope of the invention as it is dened by the following claims.

Weclaim: y

1. `Sheet engraving gum vcomprising an impression layer of removable resilient material selected from a group consisting of natural and synthetic rubber compositions, said layer lhaving an impression face and a back face defining a stripping level, and a substantially inextensible backing therefor, said backing comprising a layer of fabric at said stripping level, a substantially nonstretchable layer of semi-hard rubber cvomposition containing vulcanizing ingredients and fibers below said fabric layer, and a barrier layer of soft-rubber composition therebetween adapted to absorb vulcanizing ingredients, whereby said barrier layer acts to retard migration of vulcanizing ingredients from said composition containing fibers to said impression layer.

2. Sheet engraving gum comprising an impression layer of removable flexible vulcanized material providing an impression face, a flexible substantially inextensible'backing therefor, said backing comprising a substantially non-stretchable layer of semi-hard composition containing avulcanizing ingredient andunwoven bers, and a barrier layer ofsoft rubber composition low in sulfur content interposed between said imfabric providing at least one stripping levelv beneath the impression layer, a substantially nonstretchable backing layer of semi-hard rubber composition containing unwoven fibers beneath said fabric layer, a reinforcing layer of fabric beneath the backing layer, and a surfacing layer of soft rubber composition beneath said reinforcing layer. l,

4. Sheetengraving gum comprising an impression layer of removable material selected from a group including natural and syntheticv rubber compositions, said layer having an impression face and a back face at astripping level, at least one layer of woven fabric providing at least one stripping level beneath the impression layer, a backing layer beneath the fabric layer comprising semi-hard rubber composition containing bers and a vulcanizing ingredient, a barrier layer of soft rubber composition of low sulfur content interposed between said backing layer and said impression layer to bar migration ofsaid vulcanizing ingredient from said backing layer to said impression layer, alreinforcing layer of fabric beneath said backing layer, and a surfacing layer of rubber composition beneath said reinforcing layer.

EDWARD A. SPRIGG. EDGAR 0. MACY. 

